docs: def obo(self):
          """str: the `Relationship` serialized in an ``[Typedef]`` stanza.
  
          Note:
              The following guide was used:
              ftp://ftp.geneontology.org/pub/go/www/GO.format.obo-1_4.shtml
          """
  
          lines = [
              "[Typedef]",
              "id: {}".format(self.obo_name),
              "name: {}".format(self.obo_name)
          ]
          if self.complementary is not None:
              lines.append("inverse_of: {}".format(self.complementary))
          if self.symmetry is not None:
              lines.append("is_symmetric: {}".format(self.symmetry).lower())
          if self.transitivity is not None:
              lines.append("is_transitive: {}".format(self.transitivity).lower())
          if self.reflexivity is not None:
              lines.append("is_reflexive: {}".format(self.reflexivity).lower())
          if self.comment:
              lines.append("comment: {}".format(self.comment))
          return "\n".join(lines)